| The thermal environment of an animal fluctuates over time and has pronounced effects on neuronal operation. For an animal to be successful, neuronal circuits must be able to adapt to changing internal and external thermal conditions to produce appropriate responses. Using electrophysiological recording techniques, I have addressed questions relating to the endogenous mechanisms of thermotolerance in the locust. The model for these studies has been a visual interneuron, the descending contralateral movement detector (DCMD). This neuron relays information from visual processing regions in the brain to motor centres in the thorax that control escape behaviours. Prior exposure to a temperature stress (heat shock, HS) has been shown to extend the operating range of neural processes. This thesis has further demonstrated that HS protects the processing of complex sensory stimuli from perturbations associated with high temperature. HS protects against a temperature-dependent decrease in the number of action potentials elicited in the DCMD in response to an approaching object. I found that HS changed the stereotyped response pattern to potentiate components that are associated with the triggering of escape behaviours. HS also alters the properties of voltage-dependent channels which underlie the AP in ways that may improve conduction reliability during high frequency activity. The thesis results showed that HS modifies DCMD responses, in part, through its effect on ascending inputs originating in the thorax. The ascending input likely acts to compensate for differences in temperature between the brain and thorax. Finally, I show that HS attenuates the effects of thermal failure on the DCMD. Therefore, I show that HS promotes the fidelity of DCMD responses at high temperature through coordinated effects on multiple aspects of DCMD function. |
